update guide structure and language

[mvllow]

This pull request updates the structure and language of the current guide. I am happy to iterate and take any feedback or hand this over if this direction is not preferred. I'm also not familiar with AsciiDoc so the syntax could possibly be improved.

The goal was to fix grammar and sentence structure / overall flow. Each section was massaged rather than completely rewriting or rethinking the entire document. Two sections were merged into one:

- A note on mission control
- A note on ‘Displays have separate Spaces’
+ macOS integration

Issue #1345 mentioned the guide and commands. This only tackles the guide, for now. If desired, I'll do a similar treatment to commands.

Ref #1345